Entering Unreal Mode

[os.hacker64]

Ok, I don't know if I am failing to enter unreal mode or there is just a weird thing with my kprint function running in it. This code will print a million flashing characters on the screen after it prints a few red text lines.

[Hangin10]

Aren't you already in protected mode by the time that code is running?

[os.hacker64]

I am trying to go to unreal mode from protected mode....
I found the problem is not with calling kprint when I didn't do that I still got all the not so pretty colors on the screen.

[Hangin10]

Oh.

your code is confusing me a bit. I think it'd be easier, if you know you're in
protected mode, to do something like:

Code: Select all

mov eax, cr0
xor eax, 1
mov cr0, eax

xor eax, eax
mov ds, ax
mov ss, ax  ; your code sets ds twice btw

;jmp I don't feel like doing the math for a long jump to fix CS
        from above 1MB anyway.

Also keep in mind that you're not going to have a terribly large amount
of space if you put an Unreal Mode kernel above 1MB.

edit: err... sorry, that code seemed rather obfuscated. I think you're
just missing the jump.. ? Do you intend to be using 32bit code or
16bit code? Unreal Mode is just real mode (16bit code) capable of using
32bit addresses.

[os.hacker64]

I shall try this out.

[os.hacker64]

That code causes a triple fault

[Hangin10]

whoops, I spent a bit editing my post and you posted while I was taking forever getting my thoughts down

[os.hacker64]

I'll add the jump.

[os.hacker64]

Nope it still triple faults.....

Edit: I'm just doing this to set VBE modes it is a protected mode kernel.

[Combuster]

(*cough*)bochs debugger(*cough*)

[os.hacker64]

I tested this on a real pc. Where can I find the preconfigured grub images?

[Combuster]

I tested this on a real pc.

So?

[Masterkiller]

If you are in protected mode just do that:

Code: Select all

MOV eax, cr0
AND al, 0xFE
MOV cr0, eax

Another one mistakes in your k-print.
1. Unreal-mode is real-mode with a chance to get access to 4GB physical memory. It is a 16-bit mode, so LODSB loads a string from DS:SI, not from DS:ESI. You should have separate print functions for real and protected mode.
2. You don't have to mov a loaded value to BL to or it, OR al, al is faster because accumulator has direct access to ALU

[os.hacker64]

That is the output, this whole time I have been testing it on a real PC, I say that it triple faults because the PC resets.

[os.hacker64]

I understand with the kprint, I'm too lazy to change it.